What is Reverse Thrust? | Airspace Explained
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- เผยแพร่เมื่อ 6 ก.ย. 2024
- Have you ever wondered how reverse thrust works? I am going to explain in this video!
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Script
Twelve hours have passed, you’ve had your dry sandwich and a meal that was most likely beef or pasta served in an aluminium bowl, when you finally arrive at your destination. The plane touches down and - what is this, the engine opens up and you are pressed against your seatbelt. You know this is caused by reverse thrust - but what is reverse thrust? Does the engine spin the other way, now blowing air forward?
Nope, it does not! Today, I am going to explain to you how reverse thrust works.
Welcome to airspace explained!
Aircraft landings are absolutely fascinating, if you ask me. I myself have performed some two thousand landings and each one of them was a thrill. The transition from flight to ground roll is the art of piloting itself and the forces involved are amazing! After the plane touches down, megajoules worth of kinetic energy have to be converted into other types energy by the brakes and the reverse thrust. Planes have highly efficient carbon brakes, but that is not why you clicked this video - let’s get into the inner workings of reverse thrust.
An airliner’s jet engine has two sections, a hot section, in which the external air is first compressed, then mixed with fuel and ignited, then this air expands and drives the internal hot stream turbine, which drives a shaft that drives the compressor, sucking in more air and completing the circle. Located outside of the hot section is - you guessed it - the cold section. The drive shaft of the hot section drives the huge fan at the front of the engine, which functions just like a propeller with many blades. This increases the engines efficiency by a lot, compared to an engine which only has a hot section.
Many people think that while reverse thrust is used, the engine reverses its direction. This would be highly inefficient if not impossible, since aircraft engines often weigh multiple tons and rotate at many thousand revolutions per minute. Instead, most aircraft use some form of reverser doors that deflect the cold section air forward and outward, resulting in a decelerating force.
Some planes have pivoting door reversers, others use a sliding mechanism, but in the end, they all do the same thing - deflect the cold stream forward. On engines that do not have cold streams, such as engines of private jets, bucket type reversers are used that close into the hot stream and deflect it forward. To actuate the thrust reversers, there is a second lever on the thrust levers that the pilots can pull back in order to pull back the thrust levers beyond the normal idle position.
So, the next time you land, you will know how reverse thrust works.
But wait, there is a question - Since planes have a way of redirecting thrust forward, wouldn’t that mean that they could theoretically drive backwards on their own? Why are planes still pushed back from the gate with tractors then?
The answer is simple, reverse thrust loses efficiency the slower the plane gets, due to some physical shenanigans that would make this video too long, so just trust me on that. At a standstill, the required amount of reverse thrust would be pretty high, which would require the engine to run at high power. This is not a good idea at the gate where a lot of personnel and machinery is present, also there may be small objects left on the ground from the boarding process that may be sucked into the engine.
There you go, now you can impress your fellow passengers the next time you land with your thrust reverser knowledge.
Very interesting, love the new casual format :)
Thank you! :)
I love reverse thrust, especially when the runway is wet and it causes loads of spray. It looks fantastic!
Enjoying these short videos on interesting subjects in the aviation World.
you are talking about fucking
Love plane landing. I like to look outside to see the wing extend, the engine start to sound louder, vibration getting stronger. It is like a mini thrill.
Wonderful, concise vid. Thank you
Most thrust comes from the fan on a turbofan engine, right? The force vector on the blades of the fan propel the engine forward. How does directing the exhaust or any air after the fan blades forward generate a force vector? Does the air "push against the air?"
Have a look at @2:10, the diagram explains how the fan air that would normally be pushed out the back is redirected forward
Some planes have hot and cold reverse like the 707 with the turbo fan has it and the C-17 has it
It sucks air in from the front of the plane and it pushes the same air back to the front, it sounds like these forces should cancel each other, how does this work? And we are just talking about the air which is sucked by the fan, the core of the engine still pushes the hot air to the back...
yes, the core still produces forward thrust, but not as much. The largest portion of thrust comes from the fan.
No, the forces don't cancel each other out :)
@@AirspaceVideos I know it works, otherwise they won't use it, I just don't understand how.... it sounds like blowing your own sail.
Think about it that way:
The hot section provides, for example, 5% forward thrust.
The cold, reversed section provided 100% reverse thrust
So you have like 95% reverse thrust.
The turning of the fan (sucking in air) alone does not provide any thrust! Only when the air is blown in a direction, thrust is generated.
that's what I thought, and why I clicked on this. The rearward thrust of the bypass is created by the forward thrust on the blades, and a backwards thrust is created by the thrust redirecting diverter. They should be the same. It obviously works, but I can't figure out what I'm missing. It's like using a fan on a sailboat.
@@JeffersonLane762100% agree. I have the same doubt. The question is: are we sure that with the reverse thrust we actually producing a total net thrust which is reversed? In other words the plane would really go backwards or it is that with the reverse thrust we are just instantly reducing a lot the net forward thrust and this plus the flaps and the wheel brakes actually brake the plane?
I suppose that all modern jet airliners are designed with reverse thrust for landing, but I have seen them land without using the reverse thrust - and rely on the brakes, (plus sometimes the spoilers). My question is; how long would a runway have to be to assure all landings would have room to stop - if no plane had reverse thrust OR brakes? 15,000? 20,000? ???
This is a tricky question - the case of total brake failure and total reverser failure is so remote that it is not covered in aviation theory, and to my knowledge it has never happened before. As far as I know, the worst case that ever was was the one of Qantas 32 (I have a video describing this flight!). They used almost 4000m of runway to stop their A380 with many failures. For the A320 and A330, the worst case is about 3400m of landing distance required!
I had a pilot once tell me his airline encouraged them to not use reverse thrust in standard landings for cost reasons. Never knew why though. Fuel costs?
Wouldn't brake maintenance increase if they get pushed harder every landing?
I would say all aircraft that have them deploy the spoilers on landing, it spoils the aerodynamic effect the wing has and puts the weight of the aircraft on the wheels
Used to be common to see a diesel 9 power out of the gate rather than wait 10 minutes for a tug to show up.
One important update. In fact commercial jets have and can push back with reverse thrust. ( can see videos on TH-cam). I speak to smaller jets such as the DC-9. MD-80 and Fokker -100. These all have bucket reversers and can an and have done a push back from the gate. This was most common with the DC-9 aircraft. th-cam.com/video/zG_u_B5d7cQ/w-d-xo.html
Perfect! Thank you!
Lv this content ❤❤
Very good!
so... it's COLD air thrust reverse on some engines?
exactly
@@AirspaceVideos Thank You!
Your the best❤🎉
Thanks
👍🏻👍🏻👍🏻
I can't take anyone who pronounces aluminum with 2 I's seriously
Oh my sweet, sweet american child
@@AirspaceVideos😂
Poorly explained
Are you an idiot?
Rude
Why?
Youre just slow
Wrong
You do not understand jet engines, poor explanation and ability to differentiate between the bypass/fan, low pressure/cold, and high pressure/hot sections
Pretty sure I do but ok
@@AirspaceVideos don't worry Rayanair sent him
I think he did ok. You need to remember he is talking to the general public that don’t know what the inside of a jet engine looks like
Hello mister I want to talk with you
Please give me a response
Do Cessna also have reverse thrust
small aircraft no, they do not have reverse thrust, it is not necessary. Some medium sized turboprops like the PC-12 have some form of reverse thrust - they use a propeller that can be set to provide reverse thrust, that's called "beta range" then.